JP2016075667A - Cooling device with cryostat and cold head having reduced mechanical coupling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling device that enables an NMR (Nuclear Magnetic Resonance) measurement with fewer disturbances caused by external vibrations to be performed.SOLUTION: A cooling device 20 has a cryostat 23 and a cold head 1, and the cryostat includes: a vacuum container 4 with a vacuum container wall 4a sealing off vacuum inside the vacuum container 4 from an environment; and a cryogenic container 2 having a cryogenic container wall 2c for a cryogenic liquid or cryogenic gas. The cryogenic container is arranged inside the vacuum container, and the cryogenic container wall 2c seals off the inside of the cryogenic container from the vacuum of the vacuum container. A room temperature part 1a of a cold head is mounted to the vacuum container wall in a vibration-damped fashion by a decoupling element 5, and a cooling arm 1b of the cold head protrudes inward an access opening 13 of a cryostat to the cryogenic container along a long-side direction axis LA. A flexible sealing section 6 is provided that connects the vacuum container wall directly or indirectly to the room temperature part of the cold head, and the flexible sealing section seals off the inside of the cryogenic container from the environment.SELECTED DRAWING: Figure 2a

Description

The present invention relates to a cooling device including a cryostat and a cold head, in particular, a cold head of a pulse tube refrigerator,
-A vacuum vessel wall, the vacuum vessel wall sealing the vacuum inside the vacuum vessel from the environment; and
-A cryogenic vessel for cryogenic liquids and / or cryogenic gases having a cryogenic vessel wall, the cryogenic vessel being arranged inside the vacuum vessel, the cryogenic vessel wall being located inside the cryogenic vessel It is sealed from the vacuum of the vacuum vessel, the room temperature part of the cold head is attached to the vacuum vessel wall by a decoupling element to dampen the vibration, and the cooling arm of the cold head is aligned along the longitudinal axis Thus, there is provided a flexible sealing portion protruding into the cryostat access opening to the cryogenic vessel and directly or indirectly connecting the vacuum vessel wall to the room temperature portion of the cold head.

  This type of cooling device is disclosed in US Pat. No. 7,287,387 (B2).

  Nuclear magnetic resonance (NMR) devices, particularly NMR spectrometers and NMR tomography devices, require strong magnetic fields that are often generated by superconducting electromagnetic coils. Superconducting electromagnetic coils must be operated at extremely low temperatures. For this reason, the electromagnetic coil is usually placed in a cryostat cryogenic tank that is filled with a cryogenic liquid, such as liquid helium. In order to maintain the operating temperature over the long term and at the same time minimize the consumption of cryogenic liquid, the cooling arm of the cold head protrudes into the cryogenic tank that draws heat. The cryogenic tank is surrounded by a vacuum tank for thermal insulation.

  NMR measurements can be disturbed by mechanical vibrations of the NMR device introduced via a cold head attached to the cryostat.

  When cooling based on the pulse tube cooling principle that is often applied, periodic pressure fluctuations of the working gas are established in the cold head. For this purpose, a control valve alternately connects a high pressure tank and a low pressure tank of working gas to the cold head. The change-over frequency of the control valve is typically about 1 to 2 Hz. Disturbance vibrations in the cold head also occur with other cooling principles (eg, Stirling, Gifford-McMahon).

  European Patent Application 0780698 (A1) describes an NMR device having a mechanical decoupling between the cooling means and the cryogenic tank.

  U.S. Pat. No. 7,287,387 (B2) discloses an apparatus for cooling a superconducting magnet in which a two-stage cold head is filled with helium and surrounded by a vacuum chamber. It protrudes. The room temperature portion of the cold head is attached to a cold head flange attached to the vacuum chamber via a spring. A bellows is placed between the cold head flange and the outer wall of the vacuum chamber to seal the vacuum tank from the environment. A bellows is also provided to connect the cold head flange to the inner chamber wall to seal the vacuum tank to the inner chamber. Oscillating mounting of the cold head on the spring minimizes the introduction of vibration into the vacuum chamber by securing the cold head on the vacuum chamber. However, the bellows that are pressurized only on one side, used to seal the vacuum chamber and the inner chamber, are still not negligible between the cold head and the vacuum chamber and between the cold head and the inner chamber. Causes mechanical coupling.

  U.S. Pat. No. 5,018,359 discloses a cryogenic cooling device in which a cold head is attached to a magnetic shield and one cooling arm of the cold head protrudes into the vacuum vessel. Coupled to two thermal radiation shields. Bellows are used between the cold head flange and the outer wall of the vacuum vessel to seal the vacuum from the environment. Also in this case, the bellows that is pressurized only on one side causes a non-negligible mechanical connection with the cold head.

  DE102004034729 (B4) discloses a cryostat configuration, in which the cold head is attached to the outer wall of the cryostat via a spring. One cooling arm of the cold head protrudes into the neck tube of the helium vessel. In order to establish a thermal coupling between the upper cooling stage of the cooling arm and the thermal radiation shield, a finned coupling surface is provided with a gas gap remaining therebetween.

  The object underlying the present invention is to present a cooling device with a further reduced mechanical coupling between the cold head and the cryostat, in particular in order to be able to perform NMR measurements with little disturbance due to external vibrations. It is to be.

  This object is achieved in a surprisingly simple and effective manner by a cooling device of the aforementioned type, characterized in that the flexible sealing part seals the interior of the cryogenic container from the environment.

  In the cooling device according to the invention, in particular, the fastener itself is attached to the vacuum chamber wall by means of a separating element so that the vibration is not introduced into the vacuum vessel by the cold head. Because the cooling arm protrudes into the access opening or into the cryocontainer, the access opening or cryocontainer is protected from losing or fouling the refrigerant (cryogenic liquid or related gas) inside the cryocontainer And must be sealed.

  In addition to the cold head inserted into the access opening (including any element rigidly coupled to the cold head), the access opening is also sealed by a flexible sealing portion. According to the invention, the latter seals the interior of the cryogenic container in which the gaseous refrigerant is stored at least partially from the environment containing air. In this connection, the gas pressure prevails on each of the two sides of the flexible sealing part, and the gas pressure of the cryocontainer and the gas pressure of the environment are at least part of each other in the flexible sealing part. Compensate. The pressure difference between the two sides is usually between 0 and 50 mbar, usually less than 25 mbar, and a slightly higher gas pressure is established in the cryogenic vessel. This prevents or at least minimizes mechanical tension on the flexible sealing portion due to gas pressure differentials. When the cold head vibrates, the flexible sealing portion then vibrates substantially freely, thereby minimizing the transfer of vibration to the cryostat. This minimizes NMR measurement disturbances using a cooling device having a superconducting magnet in a cryogenic vessel.

  Only the mechanical connection between the cold head and the cryostat is realized via one or more flexible sealing parts that are exposed to the gas pressure of the cryogenic vessel and also to the ambient pressure, and via the separating element It is preferred that In accordance with the present invention, it is particularly flexible to be exposed to vacuum and also to ambient or cryogenic vessel gas pressure and cause considerable mechanical coupling due to the required solidity and resulting mechanical tension. There is no mechanical connection between the cold head and the cryostat via the permeable sealing element.

  According to the present invention, the cold head (including all elements rigidly coupled to the cold head) is not involved in sealing the vacuum vessel. Rather, the vacuum vessel is hermetically sealed independent of the cold head (and all elements that are rigidly coupled to the cold head). Thus, there is no need to construct a flexible sealing portion to seal the vacuum vessel from the environment or from the cryogenic vessel. Thus, the vacuum vessel or its wall can be designed to be completely rigid.

  In summary, according to the present invention, the flexible sealing portion hermetically connects the room temperature portion of the cold head to the cryostat (typically in the transition region from the cryogenic vessel wall to the vacuum vessel wall) The pressure prevails outside the sealing part (typically about 1000 mbar) and the cryogenic vessel pressure prevails inside (usually about 1020 mbar, the cryocontainer contains the cryogenic liquid above which the associated gas For example, helium or nitrogen). Due to the small pressure difference, the sealing part may be established to be very flexible and substantially free of mechanical tension, so that very little mechanical between the cold head and the vacuum vessel Can be combined.

Preferred variants of the invention In one preferred embodiment of the cooling device of the invention, the cryogenic vessel is liquid helium and also gaseous helium at a pressure between 950 mbar and 1100 mbar, preferably between 1015 mbar and 1050 mbar. Including. By using helium as a refrigerant, a temperature of 4.2K can be obtained in the cryogenic vessel. The helium pressure in the cryocontainer (including the part belonging to the cryocontainer, for example the neck tube, close to the cryostat access opening) is usually kept constant and the helium pressure is the ambient pressure (or This expected variation range is selected to be slightly above. The latter also prevents helium contamination by air. An alternative cryogenic liquid or alternative gas is nitrogen.

  In another preferred embodiment, the flexible sealing portion connects a first mounting portion on the vacuum vessel wall and a second mounting portion on the cold section of the cold head, which are on the longitudinal axis. On the other hand, they are arranged at the same level. In other words, the flexible sealing portion constructs a seal that is perpendicular to the longitudinal axis, which typically extends in the vertical direction, which typically results in a horizontal seal. Is brought about. This prevents temperature gradients along the encapsulant and thus prevents the encapsulant from becoming brittle.

  In one preferred embodiment, the vacuum vessel wall is designed to be completely rigid. This is particularly simple, stable and safe. Furthermore, the cryogenic vessel has no low frequency vibration mode or only a few low frequency vibration modes, which is suitable for preventing interference with NMR measurements.

  In one advantageous embodiment, the flexible sealing part is formed by an elastomeric material, in particular a rubber plastic diaphragm. Plastic diaphragms are robust and inexpensive to manufacture.

  In another preferred embodiment, the flexible sealing portion is designed as a rolling diaphragm. This has been found to be favorable in practice. The rolling diaphragm builds a relatively long flexible seal in a relatively small space, which provides good insulation of typical vibrations, for example about 1 to 2 Hz.

  In one preferred embodiment, a thermal radiation shield is disposed between the vacuum vessel wall and the cryogenic vessel wall in the vacuum vessel, and the cooling stage of the cooling arm is thermally coupled to the thermal radiation shield. A first coupling element having a first coupling surface is formed on the cooling stage of the cooling arm, and a second coupling element having a second coupling surface is formed on the thermal radiation shield; The two coupling surfaces are arranged opposite to each other in the cryogenic vessel, but a gap remains between the first coupling element and the second coupling element. In order to cool the thermal radiation shield and at the same time prevent mechanical coupling of the cold head to the thermal radiation shield, sufficient heat exchange is performed through the (narrow) gap (mainly the gas placed in the gap). Can occur between two coupling elements. This further contributes to preventing vibration in the cryostat. In addition to the cooling stage coupled to the thermal radiation shield, there is usually an even cooler cooling stage on the cooling arm that is typically used to actually cool the refrigerant (eg, by reliquefaction of the gaseous refrigerant). It should be noted. The coupling element is usually an annular design.

  In an advantageous further development of this embodiment, the first coupling surface has an axial protrusion and / or an axial recess and the second coupling surface is a mirror inversion axial recess and And / or a mirror reversal axial protrusion. The protrusions and recesses increase the binding surface area within the small area. Usually there are 2 to 4 protrusions or 2 to 4 recesses per coupling surface.

  The first coupling surface advantageously has axially symmetrical teeth with an annular axial protrusion and an annular axial recess, and the second coupling surface is an annular axial recess and an annular axial protrusion. And a mirror-reversed axially symmetric tooth portion provided. The axial symmetry prevents misalignment of the coupling surface due to rotation of the cold head about the longitudinal axis. It should be noted that the axial protrusions typically have an axial height of 1 cm to 5 cm.

  Each annular axial protrusion and each annular axial recess preferably has a triangular shape in the longitudinal part, in particular at an inclination angle between 10 ° and 30 ° with respect to the longitudinal direction. This is practically between the cold head (or first coupling element) and the cryogenic vessel wall (or second coupling element), especially in the case of cold head vibrations transverse to the longitudinal direction. Has been found to be useful for preventing contact. Usually there are 2 to 4 teeth per coupling element.

  In another preferred further development, if the cold head does not flex, the gap width in the direction with minimal separation between the first and second coupling surfaces is 0.8 mm and 4.0 mm. Between. With this gap width there is generally enough play for the cold head to prevent contact with the cryocontainer wall, while there is sufficient thermal coupling between the coupling surfaces.

In another preferred embodiment, the separating element mounted by the cold head has a natural frequency f0 with f0 ≦ 0.75 Hz, preferably f0 ≦ 0.5 Hz. These natural frequencies have values well below the typical disturbance frequency due to pressure fluctuations in a pulse tube refrigerator (about 1.5 Hz) to effectively isolate them. f0 is substantially less than 1 / (2 ^ 0.5) ^* fext if the disturbance is a disturbance frequency, in particular, the switching frequency of the control valve of the pulse tube refrigerator to which the cold head belongs (change over frequency). Is preferred. In general, f0 is set to be smaller than 0.5 / (2 ^ 0.5) ^* fext.

  According to a preferred embodiment, the separating element minimizes the excitation of the cryostat by the cold head in only two orthogonal directions perpendicular to the longitudinal axis, and the connection line from the control valve to the cold head is exclusive. In such a way that it is straight and perpendicular to the longitudinal axis. The cold head is designed to be stationary with respect to the cryostat in the longitudinal direction. The orientation of the connection line prevents the introduction of vibrations along the longitudinal axis. This embodiment is inexpensive to build.

  In one alternative advantageous embodiment, the separating element minimizes the excitation of the cryostat by the cold head and also the movement of the cold head parallel to the longitudinal direction in both two orthogonal directions perpendicular to the longitudinal direction. To do. This dampens all kinds of introduced vibrations regardless of the orientation of the connection line from the control valve to the cold head.

  In one preferred further development of this embodiment, it is defined by a rigid wall, a further flexible sealing part, in particular a further rolling diaphragm, and a pressure plate held by the flexible sealing part. A compensation chamber is established on the cooling device, the rigid wall is rigidly coupled to the cryostat vacuum vessel wall, and the pressure plate is mechanically coupled to the cold head along the longitudinal axis, or Formed by a cold head, the pressure plate is located opposite the room temperature flange surface of the cold head that also seals the access opening, this means depending on the pressure in the cryogenic vessel. Is provided for adjusting the pressure in the compensation chamber in particular to be equal to the pressure in the cryogenic vessel. This configuration compensates for ambient pressure fluctuations due to, for example, weather changes. The cold head is exposed to a small force due to the gas pressure in the cryocontainer that (generally) tries to push the cold head out of the access opening. The amount of this force depends on the pressure difference between the cryogenic vessel and the surroundings. In order to keep the cold head in a fixed position relative to the cryostat (relative to the longitudinal axis), a counter force can be applied to the cold head via the pressure plate and the gas pressure in the compensation chamber.

  The means advantageously includes a pressure compensation line connecting the cryogenic vessel to the compensation chamber. In this way, the pressure in the compensation chamber can be established in a very simple and inexpensive manner, depending on the gas pressure in the cryogenic vessel. If the pressure compensation line has a sufficiently large cross section, the pressure in the compensation chamber will then be approximately equal to the pressure in the cryogenic vessel.

  It is preferable that the surface of the pressure plate and the surface of the cold head room temperature flange are equal in size and arranged in parallel to each other. For this reason, the gas-pressure-induced force on both sides of the cold head can be easily offset.

  The pressure plate is advantageously separated from the cold head, in particular a rolling means formed by a single bearing ball or a plurality of bearing balls is arranged between the pressure plate and the rear side of the cold head. Yes. The rolling means allows for the rotation of the cold head relative to the pressure plate about the longitudinal axis and a simple tilting movement of the cold head mainly relative to the pressure plate or on the cryostat, so that in particular the vibration of the cold head Realize good insulation. In the case of a single bearing ball, the cold head can be tilted about any tilt axis perpendicular to the longitudinal direction. The rolling means may include a plurality of bearing balls, for example, three bearing balls or rolling bearing races.

  In one preferred embodiment, a connection line between the control valve and the cold head is connected to the cold head at a contact point, the contact point being away from the first coupling element in the direction of the longitudinal axis. , Spaced from the center of gravity of the cold head. In this way, the amplitude of the cold head can be minimized, especially in the toothed coupling area. It should be noted that the behavior of the separating element should be taken into account in order to determine the optimum position of the contact point relative to the direction of the longitudinal axis. If necessary, the optimal position of the contact point can be determined by experimentation.

  In another advantageous embodiment, the cold head comprises a cooling stage and a further cooler cooling stage, the cooling stage being substantially in the position of the thermal radiation shield in the direction of the longitudinal axis, and the further cooler cooling stage. Protrudes into the cryogenic vessel deeper than the cooling stage. A thermal radiation shield disposed within the vacuum vessel and surrounding the cryogenic vessel reduces heat input into the cryogenic vessel. The arrangement of the cooling stage at the location of the heat radiation shield realizes a compact structure, and the thermal coupling of the heat radiation shield to the cooling stage can be realized efficiently over a short distance. A further cooling stage realizes an efficient reliquefaction of the cryogenic liquid.

  In another advantageous embodiment, the separating element is designed as a “negatively rigid” insulating element. “Negatively stiff” insulating elements may be specifically designed as described in US 2014/0048989 (A1) or also in US Pat. No. 5,178,357 (A). . These decoupling elements exhibit large deflections when weakly excited and at a natural frequency of less than 1 Hz, especially also in the range of less than 0.4 Hz, which can hardly be achieved with conventional metal springs or rubber bearings in a similar compact structure. May be designed. Also, a separation element based on an air suspension may be used alternatively, for example.

  The present invention also relates to the use of the above-described cooling device of the invention in an NMR measurement configuration, wherein the cryogenic vessel includes an electromagnetic coil, the sample is disposed in the room temperature hole of the cryostat, the sample undergoes NMR measurement, The NMR spectrum of the sample is recorded. The electromagnetic coil, which may be wound with a high temperature superconducting material and / or a low temperature superconducting material, is cooled by the cryogenic liquid in the cryogenic vessel, and the cold head does not interfere with the NMR measurement by the introduced vibration. Maintain the operating temperature of the cryogenic liquid.

  Further advantages of the invention can be drawn from the description and the drawings. The features described above and below may be used in accordance with the present invention either individually or collectively in any combination. The illustrated and described embodiments are not to be understood as a comprehensive enumeration but have exemplary characteristics for illustrating the present invention.

  The invention is illustrated in the drawing and is explained in more detail in connection with an embodiment.

FIG. 3 is a schematic side view of an NMR measurement configuration including a cooling device of the invention and a control valve disposed separately from the cooling device of the invention. FIG. 3 is a schematic top view of an NMR measurement configuration including a cooling device of the invention and a control valve disposed separately from the cooling device of the invention. 1 is a schematic longitudinal sectional view of an embodiment of an inventive cooling device with a compensation chamber. FIG. 1 is a schematic partially cut perspective view of an embodiment of an inventive cooling device with a compensation chamber. FIG. 1 is a schematic partial cut perspective view of an embodiment of an inventive cooling device with a cold head fixed in a direction along a longitudinal axis. FIG.

  FIGS. 1 a and 1 b show side and top views of an NMR measurement configuration 33 that includes the inventive cooling device 20.

  In this case of a pulse tube refrigerator, the cooling device 20 includes a cryostat 23 and a cold head 1, with one cooling arm of the cold head 1 being inserted into the access opening of the cryostat 23 (the latter being shown). In this connection, see FIGS. 2a and 2b). The cold head 1 is attached to the outside of the cryostat 23 via a separating element 5. The cold head 1 is further connected to the control valve 21 via the connection line 14. A separate control valve 21 on the support 22 alternately connects a low pressure tank and a high pressure tank (not shown) of working gas to a cold head 1 having a frequency of about 1 to 2 Hz via a connection line 14. Thereby, the cold head 1 is cooled. In this case, the connection line 14 is guided in a straight line and is perpendicular to the longitudinal axis LA of the cold head 1 (in this case perpendicular), along which this cooling arm extends.

The cryostat 23 has a room temperature hole 30 for accommodating the sample 31 to be measured. The superconducting electromagnetic coil 32 generates a strong uniform magnetic field B ₀ at the position of the sample 31. An RF pulse is irradiated into the sample 31 by a radio frequency (RF) resonator 34, and the RF response of the sample 31 is read out.

  2a and 2b show a longitudinal cross-sectional view and a partial cut-away perspective view of an embodiment of a cooling device 20 in the region of the cold head 1, as may be used, for example, in the configuration of FIG. 2a and 2b show only a small part of the cryostat 23, and in particular, the part of the cryostat 23 arranged further below is omitted in each case for the sake of simplicity. Should be noted.

  The cooling device 20 includes a cold head 1 having a room temperature portion 1a and a cooling arm 1b. The cooling arm 1b protrudes into the access opening 13 of the cryostat 23 connected to the cryogenic vessel 2 along the longitudinal axis LA. The room temperature portion 1a is mounted on the outside of the cryostat 23, that is, on the vacuum vessel wall 4a via the rod 17 and the separating element 5 so as to attenuate vibrations. In the illustrated embodiment, this causes vibrations in two orthogonal directions x, y that are oriented perpendicular to the longitudinal axis LA, and vibrations that are directed in the direction z along the longitudinal axis LA. Is insulated from the cryostat 23. In this case, the separating element 5 is designed as a “negatively rigid” insulating element.

  The cryocontainer 2 is at least partially filled with a cryogenic liquid, such as liquid helium (not shown in detail), and above this in the cryocontainer 2 is an associated gas, such as gaseous helium. Has been placed. The cryogenic container 2 has a lower main portion 2a (not shown in detail, see FIG. 1a) in which a superconducting electromagnetic coil for NMR measurement is arranged, and a cooling arm 1b protrudes therein. It should be noted that the upper neck tube-like portion 2b is included.

  The access opening 13 is sealed by a lower side of the room temperature portion 1a of the cold head 1 and a flexible sealing portion 6 designed in this case as a rolling diaphragm. The flexible sealing part 6 is on the outside, on the inside of the first mounting part 27 of the vacuum vessel wall 4a (here merged with the cryogenic vessel wall 2c), on the inside, the second of the room temperature part 1a of the cold head 1a. It is being fixed to the attachment part 26 of this. The mounting parts 26, 27 are arranged at the same level with respect to the direction of the longitudinal axis LA so that the flexible sealing part 6 is not exposed to any significant temperature gradient but is completely substantially at room temperature. ing. The flexible sealing part 6 is exposed to the gas pressure of the cryogenic vessel 2 on the lower side and to the ambient pressure on the upper side.

  The vacuum vessel 4 is disposed so as to surround the cryogenic vessel 2, and the inside is a vacuum. A thermal radiation shield 3 is disposed between the vacuum vessel wall 4a and the lower portion of the cryogenic vessel wall 2c (and, within the scope of the present invention, a plurality of thermal radiation shields may be provided in the vacuum vessel 4). It should be noted that there will be). The cooling stage 15 of the cold head 1 is thermally coupled to the thermal radiation shield 3 in a non-contact manner via two coupling elements 24, 25. The first coupling element 24 is attached to the cooling stage 15, and the second coupling element 25 is attached to the thermal radiation shield 3 in which the thermal radiation shield projects through the cryogenic vessel wall 2c. The first coupling surface 24a of the first coupling element 24 is annularly serrated and has three protrusions having a triangular cross section. The second coupling surface 25a of the second coupling element 25 is also annularly serrated and has three protrusions having a triangular cross section. The side surfaces of the protrusions are all inclined with respect to the longitudinal axis LA at an angle α of about 20 °. The protrusions of the coupling surfaces 24a, 25a are engaged in each other, but a gap remains between the coupling surfaces 24a, 25a. In this case, the gap width SB (perpendicular to the side surface of the protrusion) is about 2 mm. Thus, the coupling elements 24, 25 do not contact each other.

  A bearing ball 9 is arranged on the flat rear side 1d of the cold head 1a. A pressure plate 10 is supported on the bearing ball 9 and is connected to the rigid wall 19 in an airtight manner by means of a further flexible sealing part 7, in this case also a rolling diaphragm. Has been. In this case, the rigid wall portion 19 is rigidly coupled to the vacuum vessel wall 4a via the rod 35. A compensation chamber 8 is defined by the rigid wall 19, the further sealing part 7 and the pressure plate 10. The compensation chamber 8 is connected to the cryogenic vessel 2 via the pressure compensation line 28 so that the gas pressure in the compensation chamber 8 is the same as that in the cryogenic vessel 2. The room temperature portion 1a of the cold head 1 is also used to seal the access opening 13, and the surface of the pressure plate 10 and the room temperature flange surface 18 have the same size. This ensures that the cold head 1 is exposed to the same force from the top (from the pressure plate 10) and from below (from the cryogenic vessel 2), regardless of the ambient atmospheric pressure. . For this reason, even if the surrounding atmospheric pressure varies, the position of the cold head 1 along the longitudinal axis LA is kept constant. It should be noted that the gas pressure in the cryogenic vessel 2 is generally kept constant. In particular, for readjustment, the gas pressure in the cryogenic vessel 2 can be increased by turning on (or strengthening) an electric heater (not shown). It can be reduced by turning off (or weakening). It should also be noted that the flexible sealing portion 6 and the further flexible sealing portion 7 may be selected to be structurally identical.

  The working gas connection line 14 to the cold head 1 has a contact point 29 on the cold head 1, and the contact point 29 is arranged along the longitudinal axis LA slightly above the center of gravity SP of the cold head 1. And thus separated from the center of gravity SP away from the first coupling element 24 along the longitudinal axis LA. This leads to an advantageous tilting behavior of the cold head 1 in the case of a pressure shock through the connecting line 14 so that the cold head 1 has a relatively small deflection amplitude in the region of the coupling elements 24, 25. The gap between the coupling surfaces 24a, 25a can be selected accordingly to be relatively small, which increases the thermal coupling and is at room temperature in the neck tube-like part 2b of the cryogenic vessel 2 Minimize heat loss due to cold gas flowing to the top towards the edges.

  In summary, the cold head 1 can be mounted to dampen vibrations to the vacuum vessel 4 via the separating element 5 using the cooling device 20 according to the invention. The cryogenic tank 2 is sealed to the cold head 1 via a substantially tensionless flexible sealing portion 6, whereby one cryogenic tank 2 or cryostat 23 and the other cold head 1. Minimize mechanical coupling between the two. For this reason, since the flexible sealing portion 6 is only used between the environment and the cryogenic container 2, the flexible sealing portion 6 can be maintained with almost no tension. In the upper first cooling stage 15, the cold head 1 is thermally coupled to the thermal radiation shield 3 in a non-contact manner via toothed coupling surfaces 24a, 25a. In the region of the main part 2a of the cryogenic vessel 2, above the liquid level of the contained cryogenic liquid, so that no further mechanical coupling is thereby introduced.

  Certain features of the cooling device 20 of the illustrated invention are described again in detail below.

  The cold head 1 has a cryostat such that its second further cooling stage 16 protrudes into the lower main part 2a of the cryogenic vessel (helium tank) 2 and its first cooling stage 15 cools the heat radiation shield 3. 23. Neither stage 15, 16 is in mechanical contact with the cryostat 23. Thermal coupling is realized (in a small range by thermal radiation) via a gas arranged above the refrigerant bath. The cold head 1 is held by a separating element 5, in this case a “negatively rigid” insulating element attached to the vacuum vessel (outer vessel) 4 of the cryostat 23. The gap between the cold head 1 and the neck tube-like part 2b of the cryogenic tank 2 in which the cold head 1 is installed has a flexible sealing part 6, in this case a rolling diaphragm. It is sealed via. The neck tube-like part 2 b is a connection part between the lower main part 2 a of the cryogenic tank 2 and the vacuum vessel 4.

  The flexible sealing part 6 and the further flexible sealing part 7 described below do not cause them to cause any unacceptably high mechanical coupling between the vacuum vessel 4 and the cold head 1. Designed to. For this purpose, the pressure difference in the diaphragm is adjusted to be relatively small at the outer atmospheric pressure (about 1000 mbar) and a slight overpressure (about 1020 mbar) in the cryogenic vessel 2. The pressure in the cryogenic vessel 2 is kept as constant as possible and is independent of atmospheric pressure. The constant pressure in the cryogenic container 2 is important for keeping the temperature of the refrigerant tank, which is important for the stability of the generated magnetic field, strictly constant.

  The decoupling element 5, or “negative stiffness” insulation element, is very “soft” in all three spatial directions (which means that small forces cause large displacements), so an inevitable weather-induced large It is believed that atmospheric pressure fluctuations will cause the cold head 1 to move to the top or bottom (if the atmospheric pressure drops, the cold head 1 will move to the top). In order to avoid this, the cold head 1 is pressurized by a mechanism from the top with a force that compensates for the change in the difference between the gas pressure in the cryogenic vessel and the atmospheric pressure. This is realized by a compensation chamber 8 which is also sealed with a flexible sealing part (diaphragm) 7. The pressure plate 10 of the chamber 8 has the same surface as the room temperature flange of the cold head 1. The chamber 8 is rigidly fixed to the vacuum vessel 4 and is connected to the cryogenic vessel 2 by a tube or a hose so that the pressure in the chamber 8 and the cryogenic vessel 2 is always the same. One or more bearing balls 9 are arranged between the cold head 1 and the pressure plate 10, which allows the cold head 1 to make a tilting movement with respect to the pressure plate 10.

  The vibration isolation properties of the flexible sealing part 6 are even better with respect to tilting motion than with translational motion. When a force is applied to the room temperature portion 1a of the cold head 1 by the connection line (rotating valve line) 14, the cold head 1 thus rotates around a point that is substantially at the center of the room temperature flange. This rotational movement is only possible because the cold head 1 can roll on the top of the sphere 9 and on the pressure plate 10.

  The gas pressure in the cryogenic container 2 having this structure should always exceed the atmospheric pressure. This prevents the introduction of impurities (eg air) in case of operational errors or in case of leakage. Furthermore, when the gas pressure in the cryogenic container 2 is too low, the pressure plate 10 can be lifted from the bearing ball 9.

  FIG. 3 shows a further embodiment of the inventive cooling device 20, similar to the embodiment of FIGS. 2a and 2b, only the differences will be described below.

  The cooling device 20 includes a cold head 1 that is rigidly attached to the detaching element 5 via a rod 17, which is attached to the cryostat 23 or this vacuum vessel wall 4a. In this case, the separating element 5 moves the rod 17 relative to the cryostat 23 and thus in the direction x, y perpendicular to the longitudinal axis LA, but not in the direction z parallel to the longitudinal axis LA, and thus the cold head 1. It is only possible to isolate the vibration.

  For this reason, the connection line 14 of the present embodiment is linearly arranged in the longitudinal axis LA so that the force transmitted to the cold head 1 by the pressure shock of the working gas does not raise or lower the cold head 1. Must be extended or connected perpendicularly to. These forces are thought to trigger vibrations along the longitudinal axis LA of the entire cryostat 23. The application of a force perpendicular to the longitudinal axis LA is easily prevented by supporting the control valve (rotary valve) on an appropriately sized support (in this case, see FIG. 1, reference numeral 22). obtain.

DESCRIPTION OF SYMBOLS 1 Cold head 1a Room temperature part 1b Cooling arm 1d Rear side (flat of cold head 1) 2 Cryogenic container, cryogenic tank 2a Lower main part 2b Upper neck tube-like part 2c Cryogenic container wall 3 Thermal radiation shielding 4 Vacuum container 4a Vacuum vessel wall 5 Detaching element 6 Flexible sealing part 7 Further flexible sealing part 8 Compensation chamber 9 Bearing ball 10 Pressure plate 13 Access opening 14 Connection line 15 First cooling stage 16 Further cooling stage 17, 35 Rod 18 Room temperature flange surface 19 Rigid wall portion 20 Cooling device 21 Control valve 22 Support portion 23 Cryostat 24 First coupling element 24a (first coupling element 24) First coupling surface 25 Second coupling element 25a ( Second coupling surface 26 (of the second coupling element 25) second mounting part 27 (of the room temperature part 1a of the cold head 1) 27 (vacuum) First mounting portion (of vessel wall 4a) 28 Pressure compensation line 29 Contact point 30 Room temperature hole 31 Sample 32 Superconducting electromagnetic coil 33 NMR measurement configuration 34 Radio frequency (RF) resonator B ₀ Strong uniform magnetic field f0 Natural frequency LA Long Direction axis SB Gap width SP (Cold head 1) center of gravity x, y, z direction α inclination

Claims (22)

A cooling device (20) comprising a cryostat (23) and a cold head (1), in particular the cold head (1) of a pulse tube refrigerator, wherein the cryostat (23)
A vacuum vessel wall (4a), wherein the vacuum vessel wall (4a) seals the vacuum inside the vacuum vessel (4) from the environment; and
A cryogenic vessel (2) for a cryogenic liquid and / or cryogenic gas having a cryogenic vessel wall (2c), the cryogenic vessel (2) being disposed within the vacuum vessel (4) The cryogenic vessel wall (2c) seals the inside of the cryogenic vessel (2) from the vacuum of the vacuum vessel (4), and the room temperature portion (1a) of the cold head (1) is separated. The cryostat is mounted on the vacuum vessel wall (4a) by an element (5) so as to dampen vibrations, and the cooling arm (1b) of the cold head (1) moves along the longitudinal axis (LA) with the cryostat. (23) through the access opening (13) and projecting into the cryogenic vessel (2), and the vacuum vessel wall (4a) directly to the room temperature portion (1a) of the cold head (1). Or a flexible sealing part to be indirectly connected The cooling device (20) provided with (6), wherein the flexible sealing portion (6) seals the inside of the cryogenic container (2) from the environment. Device (20).   Cooling according to claim 1, characterized in that the cryogenic vessel (2) comprises liquid helium and gaseous helium at a pressure of between 950 mbar and 1100 mbar, preferably between 1015 mbar and 1050 mbar. Device (20).   The flexible sealing portion (6) attaches the first mounting portion (27) on the vacuum vessel wall (4a) to the second mounting on the room temperature portion (1a) of the cold head (1). 3. Cooling device (20) according to claim 1 or 2, characterized in that it connects to a part (26) and they are arranged at approximately the same level with respect to the longitudinal axis (LA).   The cooling device (20) according to any one of claims 1 to 3, characterized in that the vacuum vessel wall (4) is designed to be completely rigid.   5. Cooling device (20) according to any one of claims 1 to 4, characterized in that the flexible sealing part (6) is made of an elastomeric material, in particular a rubber plastic diaphragm.   6. Cooling device (20) according to any one of the preceding claims, characterized in that the flexible sealing part (6) is designed as a rolling diaphragm. A thermal radiation shield (3) is disposed between the vacuum vessel wall (4a) and the cryogenic vessel wall (2c) in the vacuum vessel (4), and a cooling stage ( 15) is thermally coupled to the thermal radiation shield (3),
A first coupling element (24) having a first coupling surface (24a) is formed on the cooling stage (15) of the cooling arm (1b);
And a second coupling element (25) having a second coupling surface (25a) is formed on the thermal radiation shield (3),
The two coupling surfaces (24a, 25a) are arranged opposite to each other in the cryogenic vessel (2), but the first coupling element (24) and the second coupling element (25) The cooling device (20) according to any one of claims 1 to 6, characterized in that a gap remains between them.   In order to enhance thermal coupling, the first coupling surface (24a) has an axial protrusion and / or an axial recess, and the second coupling surface (25a) has a mirror inversion axial recess and / or The cooling device (20) according to claim 7, characterized in that it has a mirror reversal axial protrusion.   The first coupling surface (24a) has an axially symmetric tooth with an annular axial protrusion and an annular axial recess, and the second coupling surface (25a) has an annular axial recess and an annular 9. Cooling device (20) according to claim 8, characterized in that it has mirror inversion axially symmetrical teeth with axial protrusions.   The annular axial projection and the annular axial recess have a triangular shape in the longitudinal section, particularly at an inclination angle (α) with respect to the longitudinal axis between 10 ° and 30 °. Item 14. The cooling device (20) according to item 9.   When the cold head 1 is not bent, the gap width (SB) in the direction in which the separation between the first coupling surface (24a) and the second coupling surface (24b) is minimum is 0.8 mm. The cooling device (20) according to any one of claims 7 to 10, characterized in that it is between 4.0 mm.   12. The separating element (5) mounted on the cold head (1) has a natural frequency f0, f0 ≦ 0.75 Hz, preferably f0 ≦ 0.5 Hz. The cooling device (20) according to any one of the preceding claims.   The separating element (5) minimizes excitation of the cryostat (23) by the cold head (1) only in two orthogonal directions (x, y) perpendicular to the longitudinal axis (LA). The connecting line (14) from the control valve (21) to the cold head (1) is arranged exclusively straight and perpendicular to the longitudinal axis (LA). A cooling device (20) according to any one of the preceding claims.   The separating element (5) moves the cold head (1) both in two orthogonal directions (x, y) perpendicular to the longitudinal axis (LA) and also parallel to the longitudinal axis (LA). 13. Cooling device (20) according to any one of the preceding claims, characterized in that excitation of the cryostat (23) by the cold head (1) is minimized. Defined by a rigid wall (19), a further flexible sealing part (7), in particular a further rolling diaphragm, and a pressure plate (10) held by said flexible sealing part (7). A compensation chamber (8) is established on the cooling device (20), the rigid wall (19) is rigidly coupled to the vacuum vessel wall (4) of the cryostat (23), The pressure plate (10) is mechanically coupled to or formed by the cold head (1) along the longitudinal axis (LA), and the pressure plate (10) Is disposed opposite the room temperature flange surface (18) of the cold head (1) which also seals the access opening (13),
And this means adjusts the pressure in the compensation chamber (8), which is dependent on the pressure in the cryogenic vessel (2), in particular to be equal to the pressure in the cryogenic vessel (2). 15. Cooling device (20) according to claim 14, characterized in that it is provided for the purpose.   16. Cooling device (20) according to claim 15, characterized in that the means comprise a pressure compensation line (28) connecting the cryogenic vessel (2) to the compensation chamber (8).   17. The surface of the pressure plate (10) and the room temperature flange surface (18) of the cold head (1) are equal in size and are arranged parallel to each other. Cooling device (20).   The pressure plate (10) is separated from the cold head (1), and in particular, rolling means formed by a single bearing ball (9) or a plurality of bearing balls (9) includes the pressure plate (10). The cooling device (20) according to any one of claims 15 to 17, characterized in that it is arranged between 10) and the rear side (1d) of the cold head (1).   A connection line (14) between the control valve (21) and the cold head (1) is connected to the cold head (1) at a contact point (29), and the contact point (29) 19. The center of gravity (SP) of the cold head (1) away from the first coupling element (24) in the direction of the longitudinal axis (LA) and being spaced from the center of gravity (SP) of the cold head (1) A cooling device (20) according to any one of the preceding claims.   The cold head (1) includes the cooling stage (15) and a further cooler cooling stage (16), the cooling stage (15) being substantially in the direction (z) of the longitudinal axis (LA). ) In the position of the thermal radiation shield (3), the further cooler cooling stage (16) further protrudes into the cryogenic vessel (2) than the cooling stage (15), A cooling device (20) according to any one of the preceding claims.   21. A cooling device (20) according to any one of the preceding claims, characterized in that the decoupling element (5) is designed as a "negatively rigid" insulating element.   The cryogenic container (2) includes an electromagnetic coil (32), the sample (31) is disposed in the room temperature hole (30) of the cryostat (23), and the sample (31) is subjected to NMR measurement. Use of the cooling device (20) according to any one of claims 1 to 21 in an NMR measurement configuration (33), characterized in that, in particular, the NMR spectrum of the sample (31) is recorded.